A new type of cathode interlayer composed of 2,6-di-tert-butyl-phenolfunctionalized perylene bisimide (PBI-2P) is successfully applied as an electron transporting layer for fused-ring nonfullerene organic solar cells (OSCs). The stable contact between these novel electron transporting layers and the representative nonfullerene acceptor Y6 greatly enhances the device stability compared to conventional amine-group containing cathode interlayers. Moreover, the easily formed biradical species in the interlayers yields rather good thickness tolerance of the PBI-2P layer in photovoltaic devices. The OSCs based on the PBI-2P interlayer show a power conversion efficiency up to 17.20% and good stability compared to amino-group functionalized interlayers. The findings demonstrate a promising design principle for cathode interlayer engineering based on pigment chromophores equipped with the 2,6-di-tert-butylphenoxy groups that are prone to form the respective ultrastable butylphenoxy radicals for stable nonfullerene OSCs.

Perylene bisimide (PBI) dyes are known as red, maroon and black pigments, whose colors depend on the close π−π stacking arrangement. However, contrary to the luminescent monomers, deep-red and black PBI pigments are commonly non- or only weakly fluorescent due to (multiple) quenching pathways. Here, we introduce N-alkoxybenzyl substituted PBIs that contain close π stacking arrangement (exhibiting dπ−π ≈ 3.5 Å, and longitudinal and transversal displacements of 3.1 Å and 1.3 Å); however, they afford deep-red emitters with solid-state fluorescence quantum yields (ΦF) of up to 60%. Systematic photophysical and computational studies in solution and in the solid state reveal a sensitive interconversion of the PBI-centred locally excited state and a charge transfer state, which depends on the dihedral angle (θ) between the benzyl and alkoxy groups. This effectively controls the emission process, and enables high ΦF by circumventing the common quenching pathways commonly observed for perylene black analogues.

Conjugation breaking by “node” structures in donor–node–acceptor (D–n–A)-type molecules conceptually enables facile tuning of their oxidation and reduction behaviors through modification of the donor (D) unit and the acceptor (A) unit independently. Herein, we demonstrate the successful synthesis of a series of D–n–A-type cross-linked polymers, termed poly-4T-PDI, poly-2T3-PDI, and poly-4T3-PDI, by an in situ electrochemical polymerization reaction on the surface of electrodes and their versatile redox properties. These polymers contain oligo-thiophene structures connected with tetrachloronated perylene diimide (PDI) units through the “N node”. The investigation of the redox behaviors of these three polymers clearly indicates that there are two reversible redox waves corresponding to the oxidation–reduction couples of PDI/PDI– and PDI–/PDI2–; however, the redox signal relating to the oligo-thiophene structures completely relies on the number and connection mode of thiophene units. Especially, poly-2T3-PDI possesses a balanced ambipolar characteristic showing approximately equivalent gravimetric capacitances of 299 F g–1 for the n-doping process and 264 F g–1 for the p-doping process, which facilitate the application of such ambipolar polymers as both cathode and anode materials in pseudocapacitors. In addition, electrochemical impedance spectroscopy indicates easy ion diffusion and fast electron transfer in the film of poly-2T3-PDI, which is attributed to the fine porous structure and the conjugated backbone of polythiophene. The current research clearly demonstrates a facile strategy to achieve balanced ambipolar polymers through conjugation breaking by the “node” structure between the electron donor and acceptor units.

Efficient long-range exciton migration and charge transport are the key parameters for organic photovoltaic materials, which strongly depend on the molecular stacking modes. Herein, we extracted the stacked structures of the archetype fused-ring electron acceptor molecule, ITIC, based on the information on four polymorphic crystals and investigated the relationship between molecular stacking modes and exciton migration/charge transport properties through the intermolecular Coulomb coupling and charge transfer integral calculation. Experimentally, the thin film texture is crystallized through a post-annealing treatment through grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements, which lead to the enhanced exciton migration through exciton–exciton annihilation in the femtosecond transient absorption (fs-TA) measurements. This work demonstrates the relationship between the molecular arrangement and the exciton migration and electron transport and highlights the significance of optimizing molecular stacking for the development of high-performance electron acceptor materials.

We synthesize three perylene bisimide-based triads with donor−acceptor−acceptor (D∼A 1 −A 2 ) architectures, in which the distance between D and A 1 is varied to study its influence on the excited state electron processes. Very different intramolecular charge transfer (D + ∼A 1 −A 2 − ) lifetimes in dichloromethane (DCM) for these three triads are revealed by steady-state and transient spectroscopies. Free-energy changes of charge transfer (CT) are calculated based on the single-crystal X-ray diffraction data and electrochemical measurements. The results show that photoinduced cascading CT comprises two competing processes in DCM (CTs in D∼A1 units and in A1−A2 units) by pumping of the A1 unit, and then the long-distance CT state is formed. The charge recombination (CR) process is restrained effectively by the increased distance between the anion and cation. This research reveals the importance of multistep cascading CTs on tuning the CT lifetime in multichromophoric systems.